It has previously been recognized that conventional chuck keys are easy to lose, or frequently become separated from their associated chucks. When a chuck key is thus unavailable, it becomes difficult or impossible to operate the chuck and replace the drill bit or other cutting tool held therein.
Earlier attempts to address the problem of lost or misplaced chuck keys have resulted in the invention of various devices designed to allow a drill operator to open or close the jaws of a conventional chuck by means of a tool other than a chuck key. One such device is disclosed in U.S. Pat. No. 2,451,565, issued to Landow on Oct. 19, 1948. The Landow chuck adapter includes a tubular member which fits tightly over the lower portion of the chuck body and is secured thereto by means of a screw inserted radially through a threaded bore in the tubular member. The screw is designed to engage one of the radial bores which are disposed about the lower portion of the chuck body for the purpose of receiving the pin of a conventional chuck key. A bevel gear rotatably mounted within an interior recess on the tubular member engages the teeth cut in the outer cylinder of the chuck, and a shaft protrudes from one end of the bevel gear to form a hub on the outer surface of the tubular member. A suitable tool such as a hexagon key may be inserted into the hub and used to turn the bevel gear, thereby rotating the outer chuck cylinder relative to the inner portion of the chuck in the same manner as if the teeth on the outer chuck cylinder were engaged by a conventional chuck key.
The Landow adapter, although providing a solution to the problem of manipulating chuck jaws without a chuck key, nevertheless contains several inherently objectionable features. The presence of the hub on the outer surface of the tubular member creates an annoying and potentially dangerous obstacle to the user when the drill is rotating during operation. Moreover, the hub itself must either be relatively small in dimension, rendering it difficult to maintain a torque on the hub sufficient to open a tightly clamped jaw, or must be of such size and weight as to throw the chuck assembly out of balance. The Landow adapter thus fails to provide a practical answer to the problem of lost chuck keys.
A second type of chuck jaw operating and closing device is disclosed in U.S. Pat. No. 4,095,811, issued to Cohen on June 20, 1978. The Cohen device utilizes a friction-fitting drive sleeve which is placed over the outer chuck cylinder and an anchor ring which is placed over the inner chuck cylinder. Studs formed on the inner surface of the anchor ring engage the chuck key pivot holes formed in the chuck inner cylinder. The drill operator grips the drive sleeve in one hand and the anchor ring in the other hand. The anchor ring and drive sleeve are then twisted in opposite directions, causing the chuck outer cylinder to rotate relative to the chuck inner cylinder to lock or unlock the chuck jaws as desired. The primary disadvantage of the Cohen device lies in the fact that the torque applied to the chuck cylinders in locking or unlocking the jaws is limited by the strength of the operator's grip on the drive sleeve and the anchor ring. There is no provision in Cohen for applying any mechanical leverage to assist in operating the chuck.
The prior art also discloses several other types of specialized chuck keys. German Pat. No. 960,409, for example, issued to Gebhardt on Mar. 21, 1957, discloses a chuck assembly comprising an outer cylinder having a toothed shoulder and a cylindrical member mounted on the chuck assembly to operate the chuck jaws when rotated relative to the outer cylinder. One end of the cylindrical member is spaced a short distance from the toothed shoulder of the outer cylinder to form a channel around the periphery of the chuck assembly. Beveled teeth resembling the teeth on the outer cylinder are circumferentially cut in the end of the cylindrical member spaced from the outer cylinder, and together with the toothed shoulder of the outer cylinder form two opposing tracks of teeth in the sides of the channel. A chuck key containing a bevel gear is inserted into the channel, causing the teeth of the bevel gear to simultaneously engage the teeth on both of the opposing tracks. When the chuck key is thereafter twisted, the cylindrical member rotates relative to the outer cylinder to operate the chuck jaw mechanism while the key travels in an opposite direction along the channel formed around the periphery of the chuck. Italian Pat. No. 506,151, issued to Pagano on Nov. 21, 1954, discloses a similar type of chuck assembly. Neither the patent to Gebhardt nor the patent to Pagano, however, teaches an efficient or practical means for opening or closing the jaws of a chuck without the use of a chuck key, wherein the means can be easily attached to existing chuck assemblies of the type employing only a single toothed outer cylinder with pivot holes on the inner cylinder for receiving a conventional chuck key. In particular, the cylindrical members of both the Gebhardt and Pagano patents are integral components of the chuck assembly itself, without which the chuck jaw mechanism could not be operated. Neither member is adapted to be quickly removed from one drill chuck and readily transferred to another as the need arises. Consequently, neither member has found any use as a substitute for conventional chuck keys in every day home and industrial settings.